Đáp án:

 $+) x=\dfrac{10}{3}\\
+)x=-4\\
+) x=\dfrac{2}{3}\\
+) x=14\\
+)  x=\dfrac{21}{10}\\
+) x=\dfrac{1}{2}\\
+) x=\dfrac{-7}{4}\\
+) x=\dfrac{-2}{15}\\
+)  x=\dfrac{5}{12}\\
+)  x=\dfrac{-1}{9}\\
+) x=\dfrac{13}{6}\\
+)  x=\dfrac{-1}{8}\\
+)  x=\dfrac{-4}{90}\\
+)  x=\dfrac{3}{4}$

Giải thích các bước giải:

 $+) \dfrac{x}{5}=\dfrac{2}{3}\Leftrightarrow x=\dfrac{2}{3}.5=\dfrac{10}{3}\\
+) \dfrac{x}{9}=\dfrac{-16}{36}=\dfrac{-4}{9}\Leftrightarrow x=\dfrac{-4}{9}.9=-4\\
+) \dfrac{3}{4}x=\dfrac{1}{2}\Leftrightarrow x=\dfrac{1}{2}.\dfrac{4}{3}=\dfrac{2}{3}\\
+) \dfrac{x-12}{4}=\dfrac{1}{2}\Leftrightarrow x-12=\dfrac{1}{2}.4=2\Leftrightarrow x=2+12=14\\
+) \dfrac{x}{3}-\dfrac{1}{2}=\dfrac{1}{5}\Leftrightarrow \dfrac{x}{3}=\dfrac{1}{5}+\dfrac{1}{2}\\
\Leftrightarrow \dfrac{x}{3}=\dfrac{2}{10}+\dfrac{5}{10}=\dfrac{7}{10}\\
\Leftrightarrow x=\dfrac{7}{10}.3=\dfrac{21}{10}\\
+) \dfrac{x}{5}+\dfrac{1}{2}=\dfrac{6}{10}\Leftrightarrow \dfrac{x}{5}=\dfrac{6}{10}-\dfrac{1}{2}\\
\Leftrightarrow \dfrac{x}{5}=\dfrac{6}{10}-\dfrac{5}{10}=\dfrac{1}{10}\\
\Leftrightarrow x=\dfrac{1}{10}.5=\dfrac{1}{2}\\
+) \dfrac{x}{3}-\dfrac{1}{4}=\dfrac{-5}{6}\Leftrightarrow \dfrac{x}{3}=\dfrac{-5}{6}+\dfrac{1}{4}\\
\Leftrightarrow \dfrac{x}{3}=\dfrac{-10}{12}+\dfrac{3}{12}=\dfrac{-7}{12}\\
\Leftrightarrow x=\dfrac{-7}{12}.3=\dfrac{-7}{4}\\
+) \dfrac{4}{5}+x=\dfrac{2}{3}\Leftrightarrow x=\dfrac{2}{3}-\dfrac{4}{5}\\
\Leftrightarrow x=\dfrac{10}{15}-\dfrac{12}{15}=\dfrac{-2}{15}\\
+) \dfrac{3}{4}-x=\dfrac{1}{3}\Leftrightarrow x=\dfrac{3}{4}-\dfrac{1}{3}\\
\Leftrightarrow x=\dfrac{9}{12}-\dfrac{4}{12}=\dfrac{5}{12}\\
+) x-\dfrac{5}{9}=\dfrac{-2}{3}\Leftrightarrow x=\dfrac{-2}{3}+\dfrac{5}{9}\\
\Leftrightarrow x=\dfrac{-6}{9}+\dfrac{5}{9}=\dfrac{-1}{9}\\
+) 2\dfrac{7}{9}-\dfrac{12}{13}x=\dfrac{7}{9}\\
\Leftrightarrow \dfrac{12}{13}x=\dfrac{25}{9}-\dfrac{7}{9}=\dfrac{18}{9}=2\\
\Leftrightarrow x=\dfrac{2.13}{12}=\dfrac{13}{6}\\
+) \dfrac{1}{2}-\dfrac{2}{3}x=\dfrac{7}{12}\\
\Leftrightarrow \dfrac{2}{3}x=\dfrac{1}{2}-\dfrac{7}{12}\\
\Leftrightarrow \dfrac{2}{3}x=\dfrac{6}{12}-\dfrac{7}{12}=\dfrac{-1}{12}\\
\Leftrightarrow x=\dfrac{-1}{12}.\dfrac{3}{2}=\dfrac{-1}{8}\\
+) \dfrac{3}{4}x+\dfrac{1}{5}=\dfrac{1}{6}\\
\Leftrightarrow \dfrac{3}{4}x=\dfrac{1}{6}-\dfrac{1}{5}\\
\Leftrightarrow \dfrac{3}{4}x=\dfrac{5}{30}-\dfrac{6}{30}=\dfrac{-1}{30}\\
\Leftrightarrow x=\dfrac{-1}{30}.\dfrac{4}{3}=\dfrac{-4}{90}\\
+) \dfrac{3}{8}-\dfrac{1}{6}x=\dfrac{1}{4}\\
\Leftrightarrow \dfrac{1}{6}x=\dfrac{3}{8}-\dfrac{1}{4}\\
\Leftrightarrow \dfrac{1}{6}x=\dfrac{3}{8}-\dfrac{2}{8}=\dfrac{1}{8}\\
\Leftrightarrow x=\dfrac{1}{8}.6=\dfrac{3}{4}$